Li-ion and/or Li-ion polymer battery with shielded leads

ABSTRACT

A battery section for a Li-ion and/or Li-ion polymer cell, comprised of: 
     a planar metal mesh layer having a body portion and a coplanar tab portion defining a battery lead extending from one edge of the mesh layer; 
     electrode film laminated to opposite surfaces of the body portion of the metal mesh layer; and 
     a protective layer on at least one side of the tab, the protective layer having a portion of the tab that is adjacent to the electrode film, the protective layer comprised of an outer polymer layer and an inner adhesive layer adhering the outer polymer layer to the portion of the tab.

This application is a divisional of U.S. patent application Ser. No.09/778,699 filed on Feb. 7, 2001, now U.S. Pat. No. 6,475,674 which is acontinuation-in-part of U.S. patent application Ser. No. 09/501,197filed on Feb. 10, 2000 now U.S. Pat. No. 6,403,262.

FIELD OF THE INVENTION

The present invention relates generally to Li-ion and/or Li-ion polymerbatteries, and more particularly, to a Li-ion and/or Li-ion polymerbattery having shielded leads to reduce the likelihood of shorting.

BACKGROUND OF THE INVENTION

Broadly stated, a Li-ion and/or Li-ion polymer cell is generallycomprised of an anode section, a cathode section and a separator layerthat is disposed between the anode section and the cathode section. Alayer of a first conductive material is disposed within or in contactwith the anode section. This layer forms what is conventionally referredto as an “anode current collector.” A second layer of a conductivematerial is disposed within or in contact to the cathode section to forma “cathode current collector.” It is conventionally known to use metalscreens or meshes or foils to form the aforementioned currentcollectors. Typically, a copper mesh is used to form the anode currentcollector, and an aluminum metal mesh is used to form the cathodecurrent collector. Current collectors are typically die-cut from sheetsof metal mesh, and each current collector includes a tab portion thatdefines a battery lead. In this respect, an anode current collector willinclude a tab to define a battery's negative lead and the cathodecurrent collector will include a tab to define a battery's positivelead.

A problem with using metal mesh as a current collector is that metalburrs or shards may be formed during the die-cutting process. Theseburrs or shards project at angles to the plane of the current collector.In the body of the cell, these burrs or shards generally do not create aproblem as the layers of metal mesh forming the respective currentcollectors are generally maintained separate from each other by therespective layers of material forming the cell. However, the tabsforming the electrical leads extend beyond the peripheries of the anodesection, cathode section and separator layers and do create a problem ofshorting, particularly in a cell having two or more cathodes. In suchcells, the leads of the cathode current collectors are typically inregistry with each other and are pressed together to form one positivebattery lead. Specifically, the aforementioned cells are enclosed withina housing or packaging. During the fabrication process, the packaging isusually sealed along the peripheral edges of the cell, thereby forcinglike leads together. In most battery designs opposite leads are offsetfrom each other so that they will not contact each other. Like leads,such as two cathode sections, are typically forced together and joined.It is at these locations where the burrs or shards are more likely topenetrate through the separator layers and short circuit the cell bycoming into contact with layers of the opposite polarity.

The present invention overcomes this problem by providing a protectivelayer on the leads of the current collector where the leads extend fromthe cell to prevent burrs or shards on the current collectors frompenetrating through the separator layer.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a Li-ionand/or Li-ion polymer cell comprised of an anode layer, a cathode layerand a separator layer that is disposed between the anode layer and thecathode layer. A first, planar metal mesh layer is adjacent the anodelayer. The first metal mesh layer has a coplanar tab extending beyondthe separator layer to define a negative lead. A second, planar metalmesh layer is adjacent the cathode layer. The second metal mesh layerhas a coplanar tab extending beyond the separator layer to form apositive lead. A first protective layer is applied on the coplanar tabof the first metal mesh layer. The first protective layer is disposedwhere the tab extends beyond the anode layer and is disposed on thesurface of the tab facing the second metal mesh layer. A secondprotective layer is applied on the coplanar tab of the second metal meshlayer. A second protective layer is disposed where the tab extendsbeyond the cathode layer and is disposed on the surface of the tabfacing the first metal mesh layer.

In accordance with another aspect of the present invention, there isprovided a Li-ion and/or Li-ion polymer cell, comprised of a firstcathode section and a second cathode section. Each cathode section has acathode current collector in contact therewith. The cathode currentcollector is comprised of a sheet of metal mesh having a tab portionthat extends outwardly from the sheet beyond the cathode section to forma cathode section lead. The cathode section lead from the first cathodesection is disposed adjacent to the cathode section lead from the secondcathode section. An anode section is disposed between the cathodesections. The anode section has an anode current collector having a tabportion that extends therefrom beyond the anode section to form an anodesection lead. A separator layer is disposed between the anode sectionand each of the cathode sections. A protective layer is applied to thetab portion of each cathode current collector where the tab portionextends from the sheet. The protective layers are disposed between thetab portions to prevent shorts when the tab portions are pressedtogether to form a single positive lead.

It is an object of the present invention to provide a Li-ion and/orLi-ion polymer cell using metal mesh as current collectors.

It is another object of the present invention to provide a cell asdescribed above that is less susceptible to failure fromshort-circuiting during fabrication.

Another object of the present invention is to provide a cell asdescribed above having protective sleeves around the battery leads inthe vicinity where the leads extend from the cell.

A still further object of the present invention is to provide a cell asdescribed above having plastic tape surrounding each lead to isolate thelead from other battery components.

These and other objects and advantages will become apparent from thefollowing description of a preferred embodiment of the invention, takentogether with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthe specification and illustrated in the accompanying drawings whichform a part hereof, and wherein:

FIG. 1 is a perspective view of a cell illustrating a preferredembodiment of the present invention;

FIG. 2 is a perspective view of a current collector from the cell shownin FIG. 1, showing a protective layer surrounding the lead extendingfrom the current collector;

FIG. 3 is a top plan view of the cell shown in FIG. 1;

FIG. 4 is a front elevational view of the cell shown in FIG. 1;

FIG. 5 is a partial, sectional view taken along lines 5—5 of FIG. 4;

FIG. 6 is an enlarged fragmentary section of the area shown in FIG. 5;

FIG. 7 is an enlarged sectional view taken along lines 7—7 of FIG. 6;

FIG. 8 is a perspective view of a laminate for use in forming a batterysection, the laminate comprised of a sheet of collector material havingelectrode films applied to the opposite sides thereof;

FIG. 9 is a perspective view of the laminate shown in FIG. 8 with stripsof protective material adjacent to the electrode films;

FIG. 10 is a perspective view of a battery section die-cut, i.e.,stamped, from the laminate shown in FIG. 9;

FIG. 11 is a top, plan view of a cell showing the tabs of batterysections formed in accordance with the steps shown in FIGS. 8-10;

FIG. 12 is a partially sectioned, elevational view of the cell shown inFIG. 11; and

FIG. 13 is a top, plan view of a bi-cell showing battery sections havingprotective layers, illustrated in the alternate embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only, and notfor the purpose of limiting same, FIG. 1 shows a battery 10 illustratinga preferred embodiment of the present invention. Battery 10 is formed ofa cell 12 contained within a package 14 (shown in phantom in thedrawings) that is formed of a flexible laminate material. Cell 12 ispreferably a lithium-based electrochemical cell. Cell 12 may be aprimary (non-rechargeable) cell or a secondary (rechargeable) cell.

In the embodiment shown, cell 12 is a “bi-cell” comprised of two cathodesections 22 and an anode section 32. Each cathode section 22 iscomprised of two layers 24 of a cathode film. The film-forming cathodelayer 24 is preferably comprised of a lithiated metal oxide activematerial, a conductive material and a binder material. A currentcollector 26 formed of a metal screen or mesh is provided between eachcathode layer 24. Each current collector 26 includes an outwardextending tab or strip 28.

Anode section 32 is comprised of two layers of an anode film having acurrent collector 36 disposed therebetween. The film-forming anodelayers 34 are preferably comprised of a carbonaceous active material, aconductive material and a binder material. Current collector 36 includesan outward extending tab or strip 38 that defines the negative lead ofbattery 10.

Between anode section 32 and each cathode section 22, a separator film42 is disposed. Separator film layer 42 is preferably formed of apolymeric matrix containing ionically conductive electrolyte.

Each cathode layer 24 preferably has a thickness of about 50 μm to about300 μm, preferably about 100 μm to about 200 μm. Each anode layer 34 hasa thickness of about 50 μm to about 300 μm, preferably about 100 μm toabout 200 μm. Each separator layer 42 has a thickness of about 10 μm toabout 75 μm, preferably about 15 μm to about 35 μm. Current collectors26, 36 are preferably formed of a metal mesh or screen having athickness of about 25 μm to about 50 μm. The overall thickness of cell12 is about 800 μm or less, and preferably about 500 μm or less.

As illustrated in FIG. 1, strips 28 of cathode current collectors 26 aredisposed in registry with each other to be joined together to define asingle positive lead of battery 10. In accordance with the presentinvention, a protective sleeve 50 is wrapped around tabs 28 of cathodecurrent collectors 26. As illustrated in FIG. 2, protective sleeve 50 isdisposed about tab 28 at the location where tab 28 extends from currentcollector 26. In this respect, a portion of protective sleeve 50 isdisposed adjacent a portion of separator film 42, as best seen in FIG.5. Protective sleeve 50 may be formed of two separate strips of materialapplied to the opposite sides of tab 28, but more preferably iscomprised of a single strip of material that is wrapped around tab 28,as illustrated in FIGS. 2 and 7. In accordance with the presentinvention, protective sleeve 50 is comprised of an outer polymer layer52 and an inner adhesive layer 54. Outer layer 52 is preferably formedof a tough, thin polymer material having high dielectric properties andthat is inert to the components forming cell 12. Various plastic tapesfind advantageous application in forming outer layer 52. Such plasticmaterials may include polyimide, polyester and the like. Polymeric outerlayer 52 preferably has a thickness of about 0.0005 inches to about0.0015 inches. The width of protective layer 52 is based upon thebattery design. As indicated above, at least a portion of protectivelayer 52 will overlay separator layers 42.

Adhesive layer 54 is preferably formed of an electricallynon-conductive, thermosetting polymer, sealing material. An adhesivematerial, such as silicone, finds advantageous use as adhesive layer 54in that this material is stable in the environment of a lithium ionpolymer battery. Other adhesive materials such as rubber or resin mayalso be used. The thickness of adhesive layer 54 is about 0.001 inchesto about 0.002 inches. The total thickness of protective layer 50 ispreferably about 0.0015 inches to about 0.0030 inches.

In accordance with the present invention, protective layer 50 may beapplied manually or by automatic or semi-automatic operations. In thisrespect, protective layer 50 may be applied to current collectors 26prior to their assembly in cell 12.

FIGS. 8-10 illustrate a method of forming a battery section having aprotective lead. The method is applicable to forming either a cathodesection or an anode section that is similar to cathode section 22 andanode section 32, as heretofore described. The method shall be describedwith respect to forming a cathode section 122. However, as will beappreciated from a further reading of the specification, the method alsofinds advantageous application in forming anode section 132. Inaccordance with the present invention, a laminate 102 is formed bylaminating a sheet of a current collector material 126 with layers 124of cathode film. Layer 126 of collector material is preferably a metalscreen, mesh or a perforated sheet having a thickness of about 25 μm toabout 50 μm. Layers 124 are preferably films comprised of a lithiatedmetal oxide active material, conductive material and a binder material.(If an anode battery section is to be formed, layers 124 are preferablyfilms comprised of a carbonaceous active material, conductive materialand a binder material). As shown in FIG. 8, film layers 124 aredimensioned such that when layers 124 are applied to layer 126, aportion 126 a of mesh 126 extends beyond the edges of film layers 124.

Following lamination of film layers 124 to collector material 126, astrip 150 of protective material is then applied to each side of portion126 a of layer 126, as shown in FIG. 9. Protective strips 150 arepositioned such that one edge of each strip 150 is adjacent to the edgeof cathode film layers 124. As shown in the drawings, protective strips150 are dimensioned such that only part of exposed portion 126 a oflayer 126 is covered. Protective strips 150 are preferably comprised ofan outer layer 152 of a polymeric material and an inner layer 154 of anadhesive material. Adhesive layer 154 is similar to that previouslydescribed. In this respect, adhesive layer 154 is preferably formed of anon-conductive, thermosetting polymeric sealing material. A siliconematerial finds advantageous use as adhesive layer 154 in that thematerial is stable in an environment of a lithium-ion battery. Rubber orresin may also be used. Outer layer 154 is preferably formed of a tough,thin polymer material having high dielectric properties and that isinert to the components of cell 112. Tapes such as polyimide andpolyester find advantageous application in forming the outer layer.

The respective layers 152, 154 are similar to those previouslydescribed, and have thicknesses as heretofore described. With protectivestrip 150 applied to battery laminate 102, a composite structure, bestseen in FIG. 9, is formed. From laminate 102, a battery section 122 isformed by die cutting, i.e., stamping, laminate 102 so as to produce abattery lead 128, best seen in FIG. 10. Lead 128 includes a firstintermediate portion 128 a that is covered by protective strip 150 andan outward, end portion 128 b that is comprised of exposed layer 126.

As indicated above, the process as heretofore described may also be usedto form an anode battery section 132. A cathode section 122 and an anodesection 132 may then be laminated together with a separator 142 to forma cell 110, as best seen in FIGS. 11 and 12. Cell 110 is what isconventionally referred to as a “single cell” and has a shielded cathodelead 128 and a shielded anode lead 138. Cell 110 is adapted to be placedwithin a package 114, shown in phantom in FIG. 12. Package 114 isadapted to be sealed about the periphery of cell 114 in a manner whereinthe edge of package 114 extends over protective strip 50 on leads 128,138. When heat and pressure are applied to seal package 114, protectivestrips 150 on leads 128, 138 prevent shorting or battery discharge bypreventing shards or burrs on metal mesh layer 126 from penetrating intocontact with a conductive surface.

FIG. 13 shows a “bi-cell” 210 similar to that shown in FIG. 1, whereincathode sections 122 with protective strips 150 on leads 128 thereof areformed by a stamping process as heretofore described. As in theembodiment shown in FIG. 1, applying protective strips 150 onto cathodeleads 128 reduces the likelihood of shorting of cathode lead 128 whenbi-cell 210 is inserted within a package 214 and the edges of package214 are sealed using heat and pressure.

FIGS. 8-10 thus illustrate an alternate method for protecting leads of abattery other than the wrapping method illustrated in FIGS. 1-7. FIGS.8-10 further illustrate a method of forming battery sections for aLi-ion or Li-ion polymer battery. In this respect, FIGS. 8-10 illustratea method of forming a battery section 122 with protected leads 128 froma single sheet laminate 102 of collector material 126 and cathode film124. As will be appreciated by those skilled in the art, the methoddisclosed in FIGS. 8-10 lends itself to a generally continuous process,wherein a generally continuous strip or web of collector material 126 ismoved along a predetermined path, and then laminated to generallycontinuous strips of cathode film layers 124 that intersect the path onopposite sides of collector material 126. Heat and pressure may beapplied to the moving layer to laminate them together. Protective strips150 may then be applied from a roll in a generally continuous fashion,thereby producing a generally continuous strip of the laminate structureshown in FIG. 9. The generally continuous laminate structure could thenbe fed into a stamping press to repeatedly stamp, i.e., die-cut, batterysections therefrom, each battery section having a field lead thereon.

The foregoing description is a specific embodiment of the presentinvention. It should be appreciated that this embodiment is describedfor purposes of illustration only, and that numerous alterations andmodifications may be practiced by those skilled in the art withoutdeparting from the spirit and scope of the invention. For example, cell12 as heretofore described, disclosed cathode section 22 and anodesection 32 as being formed from layers of generally solid material. Itshall be appreciated by those skilled in the art that cathode sections22 may be formed of a single layer of a viscous material having cathodecurrent collectors embedded therein. Likewise, anode section 32 may beformed of a single layer of a viscous material having anode currentcollector 36 embedded therein. It is intended that all suchmodifications and alterations be included insofar as they come withinthe scope of the invention as claimed or the equivalents thereof.

Having described the invention, the following is claimed:
 1. A batterysection for a Li-ion and/or Li-ion polymer cell, comprised of: a planarmetal mesh layer having a body portion and a coplanar tab portiondefining a battery lead extending from one edge of said mesh layer;electrode film laminated to opposite surfaces of said body portion ofsaid metal mesh layer; and a protective layer on at least one side ofsaid tab, said protective layer having a portion of said tab that isadjacent to said electrode film, said protective layer comprised of anouter polymer layer and an inner adhesive layer adhering said outerpolymer layer to said portion of said tab.
 2. A battery section asdefined in claim 1, wherein said protective layer is on both sides ofsaid tab.
 3. A battery section as defined in claim 2, wherein said outerpolymer layer has a thickness between about 0.0005 inches and about0.0015 inches.
 4. A battery section as defined in claim 3, wherein saidouter polymer layer is comprised of polyimide.
 5. A battery section asdefined in claim 3, wherein said outer polymer layer is comprised ofpolyester.
 6. A battery section as defined in claim 4, wherein saidinner adhesive layer is comprised of silicone.